System and Method for Two-way Relaying with Beamforming

ABSTRACT

A system and method for two-way relaying with beamforming are provided. A method for relay operations includes estimating communications channels between a relay and communications devices coupled to the relay, storing data contained in the transmissions, storing data contained in the transmissions, precoding a transmission including a subset of the stored data with a precoding matrix, and transmitting the precoded transmission. The estimating is based on transmissions made by the communications devices in the subset of communications devices, and the precoding matrix is based on estimates of the communications channels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/354,641, entitled “System and Method for Two-way Relaying withBeamforming,” filed on Mar. 15, 2019, which is a continuation of U.S.patent application Ser. No. 15/606,693, entitled “System and Method forTwo-Way Relaying With Beamforming,” filed on May 26, 2017, (now U.S.Pat. No. 10,256,873, issued on Apr. 9, 2019), which is a divisional ofU.S. patent application Ser. No. 13/088,055, entitled “System and Methodfor Two-way Relaying with Beamforming,” filed on Apr. 15, 2011, (nowU.S. Pat. No. 9,686,000, issued Jun. 20, 2017) which applications arehereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to digital communications, andmore particularly to a system and method for two-way relaying withbeamforming.

BACKGROUND

A relay node (RN), or simply relay, is considered as a tool to improve,e.g., the coverage of a base station, group mobility, temporary networkdeployment, the cell-edge throughput and/or to provide coverage in newareas. The RN is wirelessly connected to a wireless communicationsnetwork via a donor cell (also referred to as a donor enhanced Node B(donor eNB or D-eNB)) through network resources donated by the D-eNB.

Generally, there may be several different types of RNs, including anamplify-and-forward RN, wherein a RN receives a transmission and thentransmits the received transmission without performing any attempt atdemodulating and/or decoding the received transmission. The RN mayreceive and transmit the transmission over different frequency bands orover different intervals of time to reduce self-interference. Anamplify-and-forward RN may amplify and/or apply additional signalprocessing on the received transmission to help improve communicationssystem performance. Another type of RN is a decode-and-forward RN: sucha RN receives a transmission, demodulates and decodes it, re-encodes andre-modulates it (possibly using a different modulation and codingscheme) and then transmits it.

Another concept applicable to RNs, either amplify-and-forward ordecode-and-forward, is a two-way RN. In a two-way RN, there is typicallyno concept of uplink and/or downlink transmission. Instead, there may bemultiple transmission phases. For example, there may be a firsttransmission phase (referred to herein as Multiple Access Phase (MA)wherein communications devices coupled to the two-way RN, such as an eNBand User Equipment (UE), transmit simultaneously, and a secondtransmission phase (referred to herein as Broadcast Phase (BC), whereinthe two-way RN broadcasts signals to the eNB and UEs coupled to thetwo-way RN.

Information theory indicates that two-way RNs may provide better linkefficiency than traditional one-way RNs (e.g., amplify-and-forward RNsand decode-and-forward RNs) that still use the concept of uplink anddownlink transmission, thereby improving overall communications systemperformance.

SUMMARY

These technical advantages are generally achieved, by exampleembodiments of the present invention which provide a system and methodfor two-way relaying with beamforming.

In accordance with an example embodiment of the present invention, amethod for relay operations is provided. The method includes estimatingcommunications channels between a relay and a subset of communicationsdevices coupled to the relay. The estimating is based on transmissionsmade by the communications devices in the subset of communicationsdevices. The method also includes storing a portion of thetransmissions, and precoding a transmission comprising a combination ofat least a subset of the stored portion of the transmissions with aprecoding matrix. The precoding matrix is based on estimates of thecommunications channels. The method further includes transmitting theprecoded transmission to the subset of communications devices.

In accordance with another example embodiment of the present invention,a method for relay operations is provided. The method includestransmitting transmission parameters to a subset of communicationsdevices coupled to a relay, receiving precoding vectors fromcommunications devices in the subset of communications devices,determining a precoding matrix from the precoding vectors, providing theprecoding matrix to communications devices coupled to the relay, storinga portion of transmissions from the subset of communications devices,and transmitting a transmission comprising a combination of at least asubset of the stored portion of the transmissions. The transmission isprecoded with the precoding matrix.

In accordance with another example embodiment of the present invention,a relay is provided. The relay includes a channel estimate unit, amemory, a precoder coefficient unit coupled to the channel estimateunit, a precoder coupled to the precoder coefficient unit and to thememory, and a transmitter coupled to the precoder. The channel estimateunit estimates communications channels between the relay and a subset ofcommunications devices coupled to the relay. The estimating is based ontransmissions made by the communications devices. The memory stores aportion of the transmissions from the communications devices, theprecoder coefficient unit determines a precoding matrix based on theestimates of the communications channels, the precoder precodes a subsetof the stored portion of the transmissions for transmission to thesubset of communications devices, and the transmitter transmits theprecoded subset of the stored portion of the transmissions.

In accordance with another example embodiment of the present invention,a method for relay operations is provided. The method includes receivingtransmissions from a first type of communications device in a subset ofcommunications devices coupled to a relay during a first interval,estimating communications channels between the relay and a subset of thefirst type of communications device transmitting to the relay, receivingtransmissions from any type of communications device in the subset ofcommunications devices coupled to the relay during a second interval,estimating communications channels between the relay and a subset of theany type of communications device transmitting to the relay during thesecond interval, and storing a portion of the transmissions from the anytype of communications device.

In accordance with another example embodiment of the present invention,a method for communications device operations is provided. The methodincludes receiving transmission parameters from a relay, determining aprecoding vector based on the transmission parameters, transmitting theprecoding vector to the relay, transmitting a first transmission to therelay, and receiving a second transmission from the relay. The secondtransmission includes a precoded combination of at least a subset of aportion of transmissions received at the relay, and the transmissionswere transmitted to the relay by a subset of communications devicescoupled to the relay.

In accordance with another example embodiment of the present invention,a communications device is provided. The communications device includesa receiver, a precoding vector unit coupled to the receiver, and atransmitter coupled to the precoding vector unit. The receiver receivestransmission parameters from a relay and receives a second transmissionfrom the relay. The second transmission includes a precoded combinationof at least a subset of a portion of transmissions received at therelay, and the transmissions were transmitted to the relay by a subsetof communications devices coupled to the relay. The precoding vectorunit determines a precoding vector based on the transmission parameters,and the transmitter transmits the precoding vector to the relay and totransmit a first transmission to the relay.

One advantage disclosed herein is that a RN may make use of precodingmethods to enhance the sum-rate performance of the RN.

A further advantage of exemplary embodiments is that a transmissionformat is provided which allows for accurate determination (e.g.,estimation) of communications channels between a RN and communicationsdevices to which it is coupled to help improve communicationsperformance. The transmission format may help the RN to determinecommunications channel information without requiring special signalingand/or processing techniques which may complicate implementation.

Another advantage of exemplary embodiments is that a distributedtechnique for determining precoding information is provided to helpreduce computational overhead at the RN and the communications devicesto which it is coupled. Reducing the computational overhead may reducematerial costs as well as operational costs of the RN and thecommunications devices.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the embodiments that follow may be better understood.Additional features and advantages of the embodiments will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1a illustrates an example communications system according toexample embodiments described herein;

FIG. 1b illustrates an example communications system with a RN operatingin a MA phase according to example embodiments described herein;

FIG. 1c illustrates an example communications system with a RN operatingin a BC phase according to example embodiments described herein;

FIG. 2a illustrates an example model of a communications system with aRN operating in a RN phase according to example embodiments describedherein;

FIG. 2b illustrates an example model of a communications system with aRN operating in a BC phase according to example embodiments describedherein;

FIG. 3a illustrates an example flow diagram of RN operations in relayingtransmissions, wherein a RN operates in a two-way relaying modeaccording to example embodiments described herein;

FIG. 3b illustrates an example flow diagram of communications deviceoperations in communications, wherein a RN operating in a two-wayrelaying mode relays communications to and from a communications deviceaccording to example embodiments described herein;

FIG. 4a illustrates an example communications system with a RN operatingin a MA phase according to example embodiments described herein;

FIG. 4b illustrates an example communications system with a RN operatingin a BC phase according to example embodiments described herein;

FIG. 5a illustrates an example structure of a transmission frameaccording to example embodiments described herein;

FIG. 5b illustrates an example structure of a transmission frameaccording to example embodiments described herein;

FIG. 6a illustrates an example flow diagram of eNB operations intransmitting according to example embodiments described herein;

FIG. 6b illustrates an example flow diagram of UE operations intransmitting according to example embodiments described herein;

FIG. 7a illustrates an example flow diagram of RN operations intransmitting to communications devices coupled to a RN, whereintransmissions are precoded with a precoding matrix W that is determinedin a distributed manner according to example embodiments describedherein;

FIG. 7b illustrates an example flow diagram of communications deviceoperations in receiving and decoding transmissions from a RN, whereinthe transmissions are precoded with a precoding matrix W that isdetermined in a distributed manner according to example embodimentsdescribed herein;

FIG. 8 illustrates an example communications device according to exampleembodiments described herein;

FIG. 9 illustrates an example communications device according to exampleembodiments described herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the current example embodiments are discussed indetail below. It should be appreciated, however, that the presentinvention provides many applicable inventive concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to exampleembodiments in a specific context, namely a communications system thatsupports RNs to help improve overall communications system performance,such as communications systems that are Third Generation PartnershipProject (3GPP) Long Term Evolution (LTE), WiMAX, IEEE 802.16, and so on,compliant.

FIG. 1a illustrates a communications system 100. Communications system100 includes a RN 105 coupled to an eNB 110 and a UE 115. According toan example embodiment, RN 105 may be operating as a two-way RN, whereinRN 105 may receive transmissions from both eNB 110 and UE 115 in a firstphase (referred to as a MA phase) and then broadcast to both eNB 110 andUE 115 in a second phase (referred to as a BC phase). As with a normalRN, RN 105 may communicate using network resources assigned by a D-eNB.For example, eNB 11 o may assign a portion of the network resources toRN 105. Denote RN 105 and UEs and/or eNBs operating with RN 105 as RN105 operates in the first phase (MA phase) and the second phase (BCphase), as communications devices participating in two-waycommunications.

FIG. 1b illustrates a communications system 120 with a two-way RNoperating in the MA phase. While operating in the MA phase, a RN 125 mayreceive transmissions from an eNB 130 (shown as signal S1) as well astransmissions from UE 135 (shown as signal S2). RN 125 may actuallyreceive transmissions from multiple UE, but only one UE is shown in FIG.1b to simplify FIG. 1b . RN 125 may simultaneously receive transmissionsfrom eNB 130 and UE 135. RN 125 may also separately receivetransmissions from eNB 130 and UE 135.

FIG. 1c illustrates a communications system 140 with a RN operating in aBC phase. While operating in the BC phase, a RN 145 may broadcast atransmission to an eNB 150 and a UE 155 (shown as signal S3). Accordingto an example embodiment, signal S3 may be a combination oftransmissions intended for eNB 150 and UE 155, e.g., S3=S1⊕S2, or thesum of the two received signals.

It is then up to eNB 150 and UE 155 to extract from S3, a transmissionintended for it. As an example, at eNB 150, eNB 150 may extract Ŝ2 (areceived version of S2 comprising S2 combined with a channel matrix Hand possibly noise) from S3 by combining it with S1, e.g., Ŝ2=S1⊕S3.

Although shown in FIGS. 1a, 1b, and 1c as being coupled to a single eNBand a single UE, a RN may be coupled to a number of eNBs and a number ofUEs. Usually, the RN may be coupled to at least one eNB, which may alsoserve as the RN's D-eNB. The RN may also be coupled to at least one UE.Therefore, the illustration and discussion of the RN being coupled to asingle eNB and a single UE should not be construed as being limiting toeither the scope or the spirit of the example embodiments.

FIG. 2a illustrates a model 200 of a communications system with a RNoperating in a MA phase. Consider a communication system with a RN 205coupled to an eNB 210 and K UEs, such as UE 215, UE 216, and UE 217,where K is a positive integer value. A communications channel between RN205 and eNB 210 may be described with a channel matrix H, whilecommunications channel between RN 205 and a k-th UE in the plurality ofUEs as g_(k).

Data, e.g., {d₁, d₂, . . . , d_(K)}, intended for the K UEs may bebeamformed by beamforming vectors, e.g., {f₁, f₂, . . . , f_(K)}, andthen transmitted by eNB 210 to RN 205. Data from a k-th UE, e.g., u_(k),may be transmitted from the k-th UE to RN 205. The combined receivedsignal at RN 205 may be expressed as

${r = {{{Hx} + {\sum\limits_{k = 1}^{K}{g_{k}u_{k}}} + n_{r}} = {{HFd} + {Gu} + n_{r}}}},$

where H is the channel matrix for a communications channel between eNB210 and RN 205, g_(k) (also G) is the channel matrix for acommunications channel between the k-th UE and RN 205, u_(k) (also u) isthe data transmitted by the k-th UE, x (also Fd) is the data transmittedby eNB 210, and n, is the noise.

FIG. 2b illustrates a model 250 of a communications system with a RNoperating in a BC phase. Consider a communication system with a RN 255coupled to an eNB 260 and a K UEs, such as UE 265, UE 266, and UE 267,where K is a positive integer value. A communications channel between RN255 and eNB 260 may be described with a channel matrix H*, whilecommunications channel between RN 255 and a k-th UE in the plurality ofUEs as g_(k)*.

Data, e.g., {d₁, d₂, . . . , d_(K)}, transmitted by eNB 260 and intendedfor the K UEs may be beamformed by beamforming vectors, e.g., {f₁, f₂, .. . , f_(K)}, and received by RN 255. Data from a k-th UE, e.g., u_(k),to eNB 260 may be transmitted from the k-th UE and received by RN 255. Aprecoded combined received signal transmitted by RN 255 may be expressedas

${\overset{\sim}{r} = {{Wr} = {{WHFd} + {W{\sum\limits_{k = 1}^{K}{g_{k}u_{k}}}} + {Wn_{r}}}}},$

where {tilde over (r)} is the precoded combined received signal at RN255, W is a precoder matrix for RN 255, r is a combined received signalat RN 255, H is the channel matrix for a communications channel betweeneNB 260 and RN 255, g_(k) (also G) is the channel matrix for acommunications channel between the k-th UE and RN 255, u_(k) (also u) isthe data transmitted by the k-th UE, x (also Fd) is the data transmittedby eNB 260, and n, is the noise. In general, precoding of the receivedsignal r is needed to help improve performance.

The precoder matrix W may be constrained to satisfy a metric on thetransmit power of the RN, for example, an average total transmit powermay be constrained by

∥{tilde over (r)}∥ ₂ ² =∥Wr∥ ₂ ² =tr(Wrr*W*)=P _(r).

Assume that a time interval between MA and BC modes is small enough sothat channel reciprocity holds, the signal received at the k-th UE isexpressible as

${y_{k} = {{{g_{k}^{*}\overset{\sim}{r}} + n_{k}} = {{{g_{k}^{*}{WHFd}} + {g_{k}^{*}W{\sum\limits_{k = 1}^{K}{g_{k}u_{k}}}} + {g_{k}^{*}{Wn}_{r}} + n_{k}} = {{g_{k}^{*}{WHf}_{k}d_{k}} + {g_{k}^{*}Wg_{k}u_{k}} + {g_{k}^{*}{WH}{\sum\limits_{i \neq k}^{K}{f_{i}d_{i}}}} + {g_{k}^{*}W{\sum\limits_{i \neq k}^{K}{g_{i}u_{i}}}} + {g_{k}^{*}{Wn}_{r}} + n_{k}}}}},$

where n_(k)˜C

(0,N₀) is AWGN at the UE. For clarity, the above expression for thesignal received at the k-th UE is labeled below

$y_{k} = {\underset{\underset{desired}{︸}}{g_{k}^{*}{WHf}_{k}d_{k}} + \underset{\underset{{self}\;\_\;{interference}}{︸}}{g_{k}^{*}{Wg}_{k}u_{k}} + \underset{\underset{{co} - {{channel}\mspace{14mu}{interference}}}{︸}}{g_{k}^{*}{W\left( {{\sum\limits_{i \neq k}^{K}{{Hf}_{i}d_{i}}} + {g_{i}u_{i}}} \right)}} + {\underset{\underset{noise}{︸}}{{g_{k}^{*}{Wn}_{r}} + n_{k}}.}}$

The self-interference term (g_(k)*Wg_(k)u_(k)) may be an importantartifact of two-way relaying operation. Assuming that a UE has completeknowledge of its channel with the RN, e.g., obtained through a prioritraining or some other technique, as well as the precoder matrix W,e.g., obtained through signaling from the RN, the self-interference maybe subtracted from y_(k). Subsequently, detection may be performed onsignal

{tilde over (y)} _(k) =g _(k) *WHf _(k) d _(k) +I _(k),

where I_(k) is the total interference-plus-noise and is expressible as

$I_{k} = {{g_{k}^{*}{W\left( {{\sum\limits_{i \neq k}^{K}{{Hf}_{i}d_{i}}} + {g_{i}u_{i}}} \right)}} + {g_{k}^{*}{Wn}_{r}} + {n_{k}.}}$

For constant channels, the interference power averaged over randomtransmissions is expressible as

${E\left\{ {I_{k}}^{2} \right\}} = {{g_{k}^{*}{W\left\lbrack {\left( {{\sum\limits_{i \neq k}^{K}{\frac{P_{d}}{K}{Hf}_{i}f_{i}^{*}H^{*}}} + {P_{u}g_{i}g_{i}^{*}}} \right) + {N_{0}I}} \right\rbrack}W^{*}g_{k}} + N_{0}}$

and a resulting SINR has the form of a generalized Rayleigh quotient

${{SINR}_{k} = \frac{g_{k}^{*}{WA}_{k}W^{*}g_{k}}{g_{k}^{*}{WB}_{k}W^{*}g_{k}}},{where}$A_(k) = Hf_(k)f_(k)^(*)H^(*) and$B_{k} = {{\sum\limits_{i \neq k}^{K}\left( {{{Hf}_{i}f_{i}^{*}H^{*}} + {\frac{KP_{u}}{P_{d}}g_{i}g_{i}^{*}}} \right)} + {\frac{{KN}_{0}}{P_{d}}\left( {1 + \frac{1}{g_{k}^{*}{WW}^{*}g_{k}}} \right)I}}$

and are N×N Hermitian matrices.

FIG. 3a illustrates a flow diagram of RN operations 300 in relayingtransmissions, wherein a RN operates in a two-way relaying mode. RNoperations 300 may be indicative of operations occurring in a RN, suchas RN 205 and RN 255, as the RN operates in the two-way relaying mode torelay information to communications devices, such as eNBs and UEs,coupled to the RN. RN operations 300 may occur while the RN is in thetwo-way relaying mode and is coupled to communications devices.

RN operations 300 may begin with the RN receiving signals(transmissions) from communications devices, such as eNBs and UEs,coupled to the RN (block 305). According to an embodiment, transmissionsfrom the communications devices may arrive at the RN substantiallysimultaneously. In other words, transmissions from the eNBs and the UEsmay all arrive at the RN at about the same time. According to anotherexample embodiment, transmissions from the communications devices mayarrive at the RN in independent phases, i.e., transmissions from theeNBs may be received in a separate phase from the transmissions from theUEs. Furthermore, if there are large numbers of UEs coupled to the RN,transmissions from the UEs may be partitioned into multiple separatephases as well. For example, a first portion (or there about) of the UEsmay transmit to the RN in a first phase, a second portion (or thereabout) of the UEs may transmit to the RN in a second phase, and soforth.

The RN may make use of signals in the transmissions to estimate (infer)communications channel characteristics and/or information aboutcommunications channels between the individual eNBs and UEs and the RN(block 307). As an example, the RN may make use of pilot signals,reference sequences, or other sequences in the transmissions receivedfrom the eNBs and the UEs to estimate communications channelcharacteristics and/or information about the communications channels.According to an example embodiment, the RN may make use of signalstransmitted by an eNB or a UE to estimate its respective communicationschannel. According to another example embodiment, instead of using aspecially transmitted signal to perform channel estimation, the RN maymake measurements of transmissions made by the eNBs and the UEs overtime to perform channel estimation.

The RN may also store a modulated and channel encoded control and amodulated and channel encoded data portion of the transmissions (as wellas other information contained in the transmissions that the RN may notuse in performing its relaying duties) (block 309). According to anexample embodiment, portions of the transmissions from the eNBs and theUEs that are not pilot signals, reference sequences, and so on, arestored. According to an example embodiment, in some situations, theentirety of the transmissions are stored if it is difficult to removethe pilot signals, reference sequences, and so on. According to anexample embodiment, the RN may store the modulated and channel encodedcontrol and data portion of the transmissions (and the otherinformation) in a buffer, a memory, a primary storage, a secondarystorage, or so forth.

The RN may use the channel estimates to construct a precoding matrix W(block 311). W may be a N×N matrix, where Nis the number of transmitantennas at the RN. According to an example embodiment, W may bedesigned to maximize a downlink sum-rate, to achieve maximal signal plusinterference to noise ratio (SINR), or so forth, for one user.Alternatively, W may be designed to meet a performance objectiverelating to the collective SINRs over multiple UEs or all UEs, such as amaximization of a weighted sum of SINRs, for example.

W may then be used to precode a transmission of the stored modulated andchannel encoded control and data portion of the transmissions (block313), which may then be transmitted (for example, broadcast) to the eNBsand the UEs (block 315). Note that the precoding matrix W may be appliedto at least a portion of a combination, e.g., sum, of received signalsfrom the eNBs and the UEs participating in the two-way communicationswith the RN, and not to the individual signal from each UE and/or eNB.Furthermore, there may be other UEs and/or eNBs that may be operatingwithin signal detection area of the RN and the UEs and/or the eNBs,however they are not participating in two-way communications with theRN.

The RN may also provide W to the eNBs and the UEs (block 317). W may bebroadcast to the eNBs and the UEs on a separate control channel or ashared control channel. W may also be transmitted on a limitedfeed-forward or feedback link. According to an example embodiment, theRN may provide W to the eNBs and the UEs in a periodic manner. Accordingto an alternative example embodiment, the RN may provide W to the eNBsand the UEs whenever it makes an update to W. According to analternative example embodiment, the RN may provide W to the eNBs and theUEs whenever it makes a specified number of updates to W. According toan alternative example embodiment, the RN may provide W to the eNBs andthe UEs whenever it receives a request to provide W.

Since W may be large in size, the RN may employ any number of techniquesto reduce the amount of information needed to provide W to the eNBs andthe UEs. For example, W may be compressed, quantized, or otherwisereduced in size prior to transmission. Additionally, the RN may providedifferential information about W instead of a complete version of W whenit provides an update of W. Furthermore, the RN may provide a functionof W to the eNBs and the UEs.

FIG. 3b illustrates a flow diagram of communications device operations350 in communications, wherein a RN operating in a two-way relaying moderelays communications to and from a communications device.Communications device operations 350 may be indicative of operationsoccurring in a communications device, such as an eNB and/or a UE, as thecommunications device receives and transmits to a RN operating in atwo-way relaying mode. Communications device operations 350 may occurwhile the communications device is coupled to a RN that is in thetwo-way relaying mode.

Communications device operations 350 may begin with the communicationsdevice transmitting signals (transmissions) to the RN (block 355).According to an example embodiment, the communications device maytransmit to the RN at substantially the same time as othercommunications devices, such as eNBs and UEs, coupled to the RN.According to another example embodiment, the communications device maytransmit to the RN at a time when other communications devices of thesame type as the communications device transmit to the RN.

The communications device may then receive a transmission from RN, wherethe transmission has been precoded with W (block 357). According to anexample embodiment, the received transmission may be a broadcast signalintended for the UEs and/or the eNB that are participating with the RNin two-way communications. The communications device may also receive W,a compressed version of W, a portion of W, a differential version of W,a function of W, or so on, from the RN (block 359). If thecommunications device receives W in an alternate form, thecommunications device may need to reconstruct W and/or otherwise updateW.

The communications device may decode the precoded transmission (block361). According to an example embodiment, the communications device maymake use of W to decode the precoded transmission. As an example, thecommunications device may make use of W as well as information regardingtheir respective communications channels to cancel self-interference andsubsequently decode the precoded transmission.

FIG. 4a illustrates a communications system 400 with a RN operating in aMA phase. Communications system 400 includes a RN 405 that is coupled toan eNB 410 and a plurality of UEs, such as UE 415 and UE 416, with RN405 operating in the MA phase. As discussed previously, during the MAphase, RN 405 receives transmissions from eNB 410 and/or the pluralityof UEs. Transmissions from eNB 410 and/or the plurality of UEs mayarrive at RN 405 substantially simultaneously, in distinct phases withtransmissions from eNB 410 (and other eNBs) arriving in a first phaseand transmissions from the plurality of UEs arriving in a second phase.Transmissions from eNB 410 and the plurality of UEs comprises data(shown as solid lines) and/or reference signals (shown as dashed lines).

FIG. 4b illustrates a communications system 450 with a RN operating in aBC phase. Communications system 450 includes a RN 455 that is coupled toan eNB 460 and a plurality of UEs, such as UE 465 and UE 466, with RN455 operating in the BC phase. As discussed previously, during the BCphase, RN 455 transmits to eNB 410 and/or the plurality of UEs bybroadcasting precoded transmissions. The transmissions may be precodedwith a precoder based on channel characteristics and/or information forcommunications channels between RN 455 and eNB 410 and/or the pluralityof UEs. Transmissions from RN 455 comprise data (shown as solid lines)and/or precoder (W) feedback (shown as dashed lines).

Generally, g_(k), the channel matrix for a communications channelbetween a k-th UE and a RN may be obtained by measuring a set of pilots,reference signals, or so forth, transmitted by the k-th UE. However, ifboth eNBs and UEs coupled to the RN are transmitting simultaneously (orsubstantially simultaneously), with the transmissions from the eNBsusually being transmitted at a significantly higher power level than thetransmissions from the UEs, then obtaining accurate and/or clean valuesfor g_(k) may be difficult. But, accurate and/or clean values for g_(k)may be important since it will help to ensure accurate determination ofW. Therefore, a frame structure that enables accurate determination ofchannel statistics and/or information between the eNBs and the UEs tothe RN is needed.

FIG. 5a illustrates a structure of a transmission frame 500.Transmission frame 500 may be representative of a transmission framereceived by a RN while the RN is operating in a MA mode. According to anexample embodiment, transmission frame 500 includes several features tohelp the RN make accurate determination of channel statistics and/orinformation between communications devices, such as eNBs and UEs,coupled to the RN. Transmission frame 500 may include time domainresources, frequency domain resources, or both time domain and frequencydomain resources.

Transmission frame 500 includes a first interval 505 wherein only eNBscoupled to the RN may transmit and a second interval 510 wherein onlyUEs coupled to the RN may transmit. First interval 505 and secondinterval 510 may be referred to as exclusive transmission intervals. Bysegregating eNB transmissions from UE transmissions, significanttransmission power level mismatches may be reduced, thereby simplifyingthe RN's task of making accurate determination of communicationschannels between the eNBs and the UEs to the RN.

According to an example embodiment, during the exclusive transmissionintervals, which ever type of communications device that is allowed totransmit may transmit signals that may assist the RN in makingdetermination of respective communications channels. For example, thecommunications devices may transmit pilots, reference sequences, and soforth. However, if a communications device has already transmitted itspilots, reference sequences, and so forth, or if the communicationsdevice has data and/or control signaling that it needs to transmit, thenthe communications device may transmit the data and/or control signalingin place of or in combination with the pilots, reference sequences, andso forth.

According to an example embodiment within second interval 510, pilots,reference sequences, and so forth, transmitted by the UEs may bemultiplexed using techniques such as code multiplexing, different phaseoffset, frequency offsets, time multiplexing, or combinations thereof.Furthermore UE specific information may also be transmitted to the RNduring second interval 510.

According to an example embodiment, it may be possible to partition theexclusive transmission intervals (first interval 505 and/or secondinterval 510, for example) into multiple parts to permit differentsubsets of a type of communications device to transmit. Partitioning arelatively large number of communications devices into multiple subsetsmay help prevent a situation wherein too many communications devices aretransmitting at the same time and potentially decrease performance.

Transmission frame 500 also includes a third interval 515 wherein botheNBs and UEs coupled to the RN may transmit. During third interval 515,eNBs and UEs may transmit as described during MA operation. According toan embodiment, during third interval 515 both eNBs and UEs may transmitdata and/or control signaling, and in some circumstances, pilots,reference signals, and so forth. Generally, since data and/or controlsignaling requirements are greater than pilots, reference sequences, andso forth, third interval 515 may be larger (for example, longer induration, wider in frequency span, or a combination of both) than firstinterval 505 and/or second interval 510.

Although shown in FIG. 5a as being time division multiplexed, firstinterval 505, second interval 510, and/or third interval 515 may be timedivision multiplexed, frequency division multiplexed, code divisionmultiplexed, or combinations thereof.

According to an example embodiment, due to the usually high transmitpower level of eNB transmissions, first interval 505 may be optional.However, to help improve communications system performance, secondinterval 510 may be a mandatory part of transmission frame 500.

Transmission frame 500 may also include guard intervals, such as guardinterval 520 and guard interval 522, to accommodate timing advance,errors in synchronization, and so forth.

Although shown in FIG. 5a as being in numerical order, i.e., firstinterval 505 before second interval 510 before third interval 515, theintervals may occur in any order.

Although transmission frame 500 is described for transmissions beingreceived by the RN, transmission frame 500 or a similar transmissionframe may be used when the RN is transmitting, i.e., the RN is operatingin the BC mode, such as transmission frame 550 shown in FIG. 5b . Whenthe RN is transmitting, a transmission frame with a first interval fortransmissions to the eNBs alone (such as in interval 555), a secondinterval for transmissions to the UEs alone (such as in interval 56 o),and a third interval for transmission to the eNBs and the UEs may beused (such as in interval 565). Furthermore, guard intervals 570 and 575may be present. According to an example embodiment, in the exclusivetransmission intervals (the first interval and/or the second interval)no network coding may be required. Furthermore, in an interval reservedfor transmissions to the UEs may be used to send data, such astransmitting W information.

FIG. 6a illustrates a flow diagram of eNB operations 600 intransmitting. eNB operations 600 may be indicative of operationsoccurring in an eNB as the eNB transmits to a RN with the RN operatingin a MA mode and the eNB is following a transmission frame format thatallows for exclusive transmission by a specific type of communicationsdevice, such as shown in FIG. 5a . eNB operations 600 may occur whilethe eNB is in a normal operating mode and while the eNB is coupled tothe RN that is operating in the MA mode.

eNB operations 600 may begin with the eNB performing a check todetermine if the RN is currently expecting transmissions only from eNBs,i.e., the RN is in an eNB only exclusive transmission interval (block605). If the RN is currently expecting transmissions only from the eNB,then the eNB may transmit (block 607). According to an exampleembodiment, the eNB may transmit pilots, reference sequences, and soforth. However, it may be possible for the eNB to also transmit dataand/or control signaling.

If the RN is not expecting transmissions from eNBs or if the eNB onlyexclusive transmission interval is over, then the eNB may perform acheck to determine if the RN is currently expecting transmissions fromeNBs as well as other communications devices, i.e., the RN is not in aneNB only exclusive transmission interval but is in an interval that willallow transmissions from eNBs (block 609). If the RN is allowingtransmissions from the eNB, then the eNB may transmit (block 611).

FIG. 6b illustrates a flow diagram of UE operations 650 in transmitting.UE operations 650 may be indicative of operations occurring in a UE asthe UE transmits to a RN with the RN operating in a MA mode and the UEis following a transmission frame format that allows for exclusivetransmission by a specific type of communications device, such as shownin FIG. 5a . UE operations 650 may occur while the UE is in a normaloperating mode and while the UE is coupled to the RN that is operatingin the MA mode.

UE operations 650 may begin with the UE performing a check to determineif the RN is currently expecting transmissions only from UE, i.e., theRN is in a UE only exclusive transmission interval (block 655). If theRN is currently expecting transmissions only from the UE, then the UEmay transmit (block 657). According to an example embodiment, the UE maytransmit pilots, reference sequences, and so forth. However, it may bepossible for the UE to also transmit data and/or control signaling.

If the RN is not expecting transmissions from UEs or if the UE onlyexclusive transmission interval is over, then the UE may perform a checkto determine if the RN is currently expecting transmissions from UEs aswell as other communications devices, i.e., the RN is not in a UE onlyexclusive transmission interval but is in an interval that will allowtransmissions from UEs (block 659). If the RN is allowing transmissionsfrom the UE, then the UE may transmit (block 661).

Although the description of FIGS. 6a and 6b focuses on operationswherein an eNB and a UE transmits to a RN following a transmit framestructure similar to one shown in FIG. 5a , the flow diagrams shown inFIGS. 6a and 6b may also apply to a RN that is transmitting to eNBs andUEs following a similar frame structure that allows for exclusivetransmission to different types of communications devices.

Determining W may be a computationally difficult problem that can placea significant burden on any one communications device, namely a RN.Therefore, there is a desire to distribute the computational burden onmultiple communications devices, such as a RN and communications devicescoupled to the RN. By distributing the computational load over multiplecommunications devices, the computational load on any one communicationsdevice may be significantly reduced. Furthermore, since W does notrequire frequent updates, communications involved in coordinating thedistribution of the computation may not become a significant performancebottleneck.

Considering the problem of designing a precoding matrix to maximize theSINR of the UEs under an average delay transmit power constraint. Givena single precoding matrix W, it may be ambitious if not infeasible toexpect to maximize every UE's SINR. A more conventional approach may beto design W so that a global system parameter is obtained, for example,maximizing the minimum SINR over the UEs. Another approach is toguarantee a minimum level of Quality of Service to the UEs, for example,requiring a minimum bound on each UE's capacity rate.

First, consider designing W such that the k-th UE's SINR is maximizedwithout regard to other UE's SINR, which may be expressed as

$\max\limits_{{{Wr}}_{2}^{2} = P_{r}}\;{{SINR}_{k}.}$

The generalized Rayleigh quotient

$\left( {{SINR}_{k} = \frac{g_{k}^{*}{WA}_{k}W^{*}g_{k}}{g_{k}^{*}{WB}_{k}W^{*}g_{k}}} \right)$

renders a solution to the above obtained from the generalizedeigen-decomposition. To simplify the notation, let {tilde over(v)}_(k)=W*g_(k). The SINR expression presented above is scale-invariantwith regard to the magnitude of W. As a consequence, the powerconstraint may be satisfied by scaling W. Relaxing the power constraint,the relay power constraint becomes

$\max\limits_{{\overset{\sim}{v}}_{k}}{\frac{{\overset{\sim}{v}}_{k}^{*}A_{k}{\overset{\sim}{v}}_{k}}{{\overset{\sim}{v}}_{k}^{*}B_{k}{\overset{\sim}{v}}_{k}}.}$

The gradient of the objective with respect to {tilde over (v)}_(k) isexpressible as

$\frac{{\partial S}{INR}_{k}}{\partial W} = {\frac{{2A_{k}{{\overset{\sim}{v}}_{k}\left( {{\overset{\sim}{v}}_{k}B_{k}{\overset{\sim}{v}}_{k}} \right)}} - {2\left( {{\overset{\sim}{v}}_{k}^{*}A_{k}{\overset{\sim}{v}}_{k}} \right)B_{k}{\overset{\sim}{v}}_{k}}}{\left( {{\overset{\sim}{v}}_{k}^{*}B_{k}{\overset{\sim}{v}}_{k}} \right)^{2}} = \frac{{2A_{k}{\overset{\sim}{v}}_{k}} - {2\left( {SINR}_{k} \right)B_{k}{\overset{\sim}{v}}_{k}}}{{\overset{\sim}{v}}_{k}^{*}B_{k}{\overset{\sim}{v}}_{k}}}$

with a necessary optimality condition of

${\frac{{\partial S}{INR}_{k}}{\partial W} = 0},$

which gives

A _(k) {tilde over (v)} _(k)=(SINR_(k))B _(k) {tilde over (v)} _(k).

By definition, the above is a generalized eigenvalue problem in thematrix pair {A_(k), B_(k)}, where SINR_(k) and {tilde over (v)}_(k)denote the eigenvalues and the eigenvectors, respectively. The equation(A_(k){tilde over (v)}_(k)=(SINR_(k))B_(k){tilde over (v)}_(k)) showsthat the extremum (stationary) points of

$\left( {\max\limits_{{\overset{\sim}{v}}_{k}}\frac{{\overset{\sim}{v}}_{k}^{*}A_{k}{\overset{\sim}{v}}_{k}}{{\overset{\sim}{v}}_{k}^{*}B_{k}{\overset{\sim}{v}}_{k}}} \right)$

are obtained as the eigenvectors of the generalized eigenvalue problemand the maximum SINR is obtained by a principle eigenvectorcorresponding to the maximum eigenvalue. Let {tilde over (v)}_(k) be thesolution for the k-th user. Substituting for the change of variable,v_(k)=W*g_(k), and reinstating the relay power constraint, the followingare necessary optimality conditions on W

W*g _(k) =v _(k)  (CI)

r*W*Wr=P _(r),  (CII)

In summary, any precoder that satisfies conditions (CI) and (CII) is (toa scaler multiple) an optimal precoder in the sense of maximizing theSINR for the k-th UE. Finding such a precoder may be difficult.

FIG. 7a illustrates a flow diagram of RN operations 700 in transmittingto communications devices coupled to a RN, wherein transmissions areprecoded with a precoding matrix W that is determined in a distributedmanner. RN operations 700 may be indicative of operations in a RN as theRN determines the precoding matrix W and uses the precoding matrix W toprecode transmissions to communications devices coupled to the RN. RNoperations 700 may occur while the RN is in a normal operating mode andis coupled to communications devices.

RN operations 700 may begin with the RN transmitting transmissionparameters to the communications devices, i.e., the eNBs and the UEs(block 705). In general, transmission parameters include channelinformation, beamforming coefficients, transmission power information,number of communications devices, and so on. Examples of transmissionparameters may be for a k-th communications device

A _(k) =Hf _(k) f _(k) *H*

and

${B_{k} = {{\sum\limits_{i \neq k}^{K}\left( {{{Hf}_{i}f_{i}^{*}H^{*}} + {\frac{KP_{u}}{P_{d}}g_{i}g_{i}^{*}}} \right)} + {\frac{KN_{0}}{P_{d}}\left( {1 + \frac{1}{g_{k}^{*}{WW}^{*}g_{k}}} \right)I}}},$

or equivalent parameters.

Although the RN may compute A_(k) and B_(k) on its own if it is aware ofH, f_(k), and g_(k). However, computational complexity may be large,especially if an iterative algorithm is being used. The computation maybe distributed to multiple communications devices to help reduce thecomputation complexity at any one communications device.

With the transmission parameters, the k-th communications device maysolve an eigenvector problem expressed as

A _(k) {tilde over (v)} _(k)=(SINR_(k))B _(k) {tilde over (v)} _(k)

for the precoding vector {tilde over (v)}_(k) and transmits {tilde over(v)}_(k) back to the RN.

The RN may receive the precoding vector {tilde over (v)}_(k) from thek-th communications device (block 707). According to an exampleembodiment, the RN may receive a precoding vector from each of thecommunications devices coupled to it, and the RN may make use of theprecoding vectors to solve for W (block 709).

Depending on the values provided by the communications devices, the RNmay solve for W with conditions CI and CII using a variety oftechniques, such as amplify-and-forward precoding, scaled inverseprecoding, unitary precoding, iteratively constrained precoding,gradient ascent, and so forth.

The RN may make use of W to precode transmissions to the communicationsdevices that are participating in two-way communications with the RN(block 711) and transmit the precoded transmissions to thecommunications devices (block 713). The RN may also provide W, updatesto W, a function of W, a compressed version of W, or so forth to thecommunications devices (block 715).

FIG. 7b illustrates a flow diagram of communications device operations750 in receiving and decoding transmissions from a RN, wherein thetransmissions are precoded with a precoding matrix W that is determinedin a distributed manner. Communications device operations 750 may beindicative of operations in a communications device, such as an eNBand/or a UE, as the communications device assists the RN in determiningthe precoding matrix W to help reduce a computational load on the RN,and then receives a transmission from the RN that has been precoded withthe precoding matrix W. The communications device may also decode theprecoded transmission from the communications device. Communicationsdevice operations 750 may occur while the communications device is in anormal operating mode and is coupled to a RN.

Communications device operations 750 may begin with the communicationsdevice receiving transmission parameters from the RN (block 755).Examples of transmission parameters at a k-th communications device mayinclude

A _(k) =Hf _(k) f _(k) *H*

and

$B_{k} = {{\sum\limits_{i \neq k}^{K}\left( {{{Hf}_{i}f_{i}^{*}H^{*}} + {\frac{KP_{u}}{P_{d}}g_{i}g_{i}^{*}}} \right)} + {\frac{KN_{0}}{P_{d}}\left( {1 + \frac{1}{g_{k}^{*}{WW}^{*}g_{k}}} \right){I.}}}$

With the transmission parameters, the communications device may solve aneigenvector problem (block 757). As an example, at the k-thcommunications device the eigenvector problem expressed as

A _(k) {tilde over (v)} _(k)=(SINR_(k))B _(k) {tilde over (v)} _(k),

and the k-th communications device may solve for the precoding vector{tilde over (v)}_(k). The communications device may send the precodingvector {tilde over (v)}_(k) to the RN (block 759).

The communications device may receive a transmission from the RN,wherein the transmission is precoded using the precoding matrix W, whichwas computed based in part on the precoding vector {tilde over (v)}_(k)provided by the communications device (block 761). According to anexample embodiment, the received transmission may be a broadcast signalintended for the UEs and/or the eNB that are participating with the RNin two-way communications.

The communications device may also receive the precoding matrix W fromthe RN (block 763). According to an example embodiment, the RN mayprovide the precoding matrix W, updates to W, a function of W, acompressed version of W, or so forth to the communications device.

The communications device may decode the precoded transmission utilizingthe precoding matrix W (block 765).

According to an example embodiment, instead of sending communicationsdevice specific transmissions parameters, such as A_(k) and B_(k), theRN may transmit non-communications device specific transmissionsparameters, such as g_(k), H, f_(k), and so forth. An advantage ofproviding non-communications device specific transmissions parameters isthat instead of dedicated signaling to each of the communicationsdevices, the RN may broadcast the non-communications device specifictransmissions parameters to all of the communications devices.

According to an example embodiment, the techniques described in FIGS. 7aand 7b do not need to be fully distributed, i.e., not everycommunications device needs to be involved in assisting the RN determinethe precoding matrix W. Rather, the RN may decide to have a subset ofcommunications devices performing the computations. For instance, ifthere are low capability communications device and there are highcapability communications devices, then the RN may decide to use onlythe high capability communications devices in performing thecomputations. The RN may perform the computations for the low capabilitycommunications devices itself.

In addition to communications device capability, the RN may selectcommunications devices based on factors such as communications deviceidle and/or busy percentages, communications device load, communicationsdevice priority, communications device performance (e.g., quality ofservice) requirements, and so forth.

Furthermore, the RN may select different subsets of communicationsdevices that it has assist it in determining the precoding matrix Wbased on a history of communications devices. As an example, the RN mayassign different subsets of communications devices over time, so thateventually, all of the communications devices would have assisted the RNin determining the precoding matrix W.

According to an example embodiment, if distributed algorithms are used,additional information, such as W(i) for the i-th iteration of W, mayalso be sent to the communications devices by the RN.

According to an embodiment, the RN may also indicate which algorithm isto be used to compute the information that will be used by the RN indetermining W. Indicating which algorithm to be used may be needed sincethe information to be provided to the RN may differ depending on thealgorithm used to determine W.

FIG. 8 provides an alternate illustration of a communications device800. Communications device 800 may be an implementation of RN.Communications device 800 may be used to implement various ones of theembodiments discussed herein. As shown in FIG. 8, a transmitter 805 isconfigured to transmit information and a receiver 81 o is configured toreceive information. Transmitter 805 includes a precoder 807 that isconfigured to precode transmissions with a precoding matrix, such asprecoding matrix W.

A channel estimate unit 820 is configured to estimate channels betweencommunications device 800 and communications devices coupled tocommunications device 800. Channel estimate unit 820 makes use ofpilots, reference sequences, and so forth, transmitted by thecommunications devices. A precoder coefficient unit 825 is configured toprocess and/or select precoder coefficients for use by precoder 807.Precoder coefficient unit 825 processes precoder coefficients based onthe channel estimates provided by channel estimate unit 820. A feedbackunit 830 is configured to provide (i.e., feedback) information, such asa precoder matrix or information about a precoder matrix, tocommunications devices. A channel information unit 835 is configured todetermine channel information about communications channels betweencommunications device 800 and communications devices coupled tocommunications device 800. A subset select unit 840 is configured toselect a subset of communications devices from communications devicescoupled to communications device 800, such as for determining theprecoding matrix W, for example. A memory 845 is configured to storeprecoding matrix (matrices), precoding vector(s), precodingcoefficient(s), channel information, channel estimates, data, etc.

The elements of communications device 800 may be implemented as specifichardware logic blocks. In an alternative, the elements of communicationsdevice 800 may be implemented as software executing in a processor,controller, application specific integrated circuit, or so on. In yetanother alternative, the elements of communications device 800 may beimplemented as a combination of software and/or hardware.

As an example, receiver 810 and transmitter 805 may be implemented as aspecific hardware block, while channel estimate unit 820, precodercoefficient unit 825, feedback unit 830, channel information unit 835,and subset select unit 840 may be software modules executing in amicroprocessor (such as processor 815) or a custom circuit or a customcompiled logic array of a field programmable logic array.

FIG. 9 provides an alternate illustration of a communications device900. Communications device 900 may be an implementation of an eNB and/ora UE. Communications device 900 may be used to implement various ones ofthe embodiments discussed herein. As shown in FIG. 9, a transmitter 905is configured to transmit information and a receiver 910 is configuredto receive information.

A decoder 920 is configured to decode transmissions received bycommunications device 900. Decoder 920 may use a precoding matrix todecode the transmissions. An interference eliminate unit 925 isconfigured to eliminate interference present in received transmissions,such as self-interference and interference from communications betweenother communications devices. A precoding vector unit 930 is configuredto solve eigenvector value problems using transmission parametersprovided by communications devices coupled to communications device 900to determine a precoding vector(s). A memory 935 is configured to storeprecoding matrix (matrices), precoding vector(s), precodingcoefficient(s), channel information, channel estimates, eigenvalues,transmission parameters, algorithm types, etc.

The elements of communications device 900 may be implemented as specifichardware logic blocks. In an alternative, the elements of communicationsdevice 900 may be implemented as software executing in a processor,controller, application specific integrated circuit, or so on. In yetanother alternative, the elements of communications device 900 may beimplemented as a combination of software and/or hardware.

As an example, receiver 910 and transmitter 905 may be implemented as aspecific hardware block, while decoder 920, interference eliminate unit925, and precoding vector unit 930 may be software modules executing ina microprocessor (such as processor 915) or a custom circuit or a customcompiled logic array of a field programmable logic array.

The above described embodiments of communications device 700 andcommunications device 800 may also be illustrated in terms of methodscomprising functional steps and/or non-functional acts. The previousdescription and related flow diagrams illustrate steps and/or acts thatmay be performed in practicing example embodiments of the presentinvention. Usually, functional steps describe the invention in terms ofresults that are accomplished, whereas non-functional acts describe morespecific actions for achieving a particular result. Although thefunctional steps and/or non-functional acts may be described or claimedin a particular order, the present invention is not necessarily limitedto any particular ordering or combination of steps and/or acts. Further,the use (or non-use) of steps and/or acts in the recitation of theclaims—and in the description of the flow diagrams(s) for FIGS. 3a, 3b,6a, 6b, 7a, and 7b —is used to indicate the desired specific use (ornon-use) of such terms.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method comprising: transmitting, by a relay,transmission parameters to a subset of communications devices coupled tothe relay; receiving, by the relay, precoding vectors fromcommunications devices in the subset of communications devices;determining, by the relay, a precoding matrix from the precodingvectors; providing, by the relay, the precoding matrix to communicationsdevices coupled to the relay; storing, by the relay, a portion oftransmissions from the subset of communications devices; andtransmitting, by the relay, a transmission comprising a combination ofat least a subset of the stored portion of the transmissions, whereinthe transmission is precoded with the precoding matrix.